Add a basic port of the Ruby combat framework

game/plugin/entity/combat/src/framework/combat_state.kt

@@ -0,0 +1,58 @@
+import MobAttributeDelegators.attribute
+import org.apollo.game.model.entity.EntityType
+import org.apollo.game.model.entity.Mob
+import org.apollo.game.model.entity.Npc
+import org.apollo.game.model.entity.Player
+import java.util.*
+
+//@todo - CombatState interface and NpcCombatState/PlayerCombatState to better drive
+// behaviours
+object CombatStateManager {
+    private val states = WeakHashMap<Mob, CombatState>()
+
+    fun stateFor(mob: Mob): CombatState {
+        return states.computeIfAbsent(mob, {
+            val combatStyle = when (mob) {
+                is Player -> mob.weapon.weaponClass.styles[mob.combatStyle]
+                is Npc -> Weapons[null].weaponClass.styles[0] // @todo
+                else -> throw IllegalStateException("Invalid type: ${mob.javaClass.name}")
+            }
+
+            CombatState(it, combatStyle.attack)
+        })
+    }
+
+    fun remove(it: Mob) {
+        states.remove(it)
+    }
+}
+
+var Mob.combatStyle: Int by attribute("combat_style", 0)
+var Mob.combatAttackTick: Long by attribute("combat_attack_tick", 0)
+
+class CombatState(private val mob: Mob, var attack: Attack) {
+    var target: Mob? by WeakRefHolder()
+
+    fun ticksSinceAttack(): Long {
+        return mob.world.tick() - mob.combatAttackTick
+    }
+
+    fun inRange(): Boolean {
+        val target = this.target ?: return false
+        val distance = mob.position.getDistance(target.position)
+        val objectType = when (attack.type) {
+            AttackType.Ranged -> EntityType.PROJECTILE
+            else -> EntityType.NPC
+        }
+
+        return distance <= attack.range /* && mob.world.collisionManager.raycast(mob.position, target.position, objectType) */
+    }
+
+    fun canAttack(): Boolean {
+        return ticksSinceAttack() >= attack.speed
+    }
+}
+
+val Mob.combatState: CombatState
+    get() = CombatStateManager.stateFor(this)
+